Teachers' unions have criticised the Welsh government's decision to introduce changes to the GCSE English language course without notice.

More prominence will now be given to the exam rather than course work and a unit is being withdrawn.

One union said it was a knee jerk reaction to the summer's GCSE English language row, when many Welsh pupils received better results after a review.

The Welsh government said it had acted swiftly to "address an injustice".

The first pupils to be affected would be those in year 10 who are sitting the exam in summer 2014 and who have already started the course.

Teachers said introducing changes to a course they had already started teaching was shocking and showed a lack of experience on behalf of the Welsh government as an exam regulator.

We do not want Welsh students to be subject to grade boundary rules determined in EnglandWelsh government

Rebecca Williams, a policy officer with Welsh teachers' union Ucac, said: "We don't mind the specific changes that are being made - I think they will be widely accepted across the profession and seen as being sensible.

"The problem is with the timing because teachers began teaching this course and students started following the course in September.

"It's an extremely unusual step for the regulator to say we're changing the specification once it's already being taught."

She said the "unspoken convention" was for teachers to be given at least a term's notice of any such changes.

"I know of at least one school that has already covered the unit that is now being withdrawn," she added.

NUT Wales has written to Education Minister Leighton Andrews to urge him to slow down on the proposed changes.

"We have received several calls from members across Wales voicing their concern that the proposed changes will have a detrimental effect on current year 10 pupils who have already started the 'old' GCSE course," said NUT Wales secretary David Evans.